What is message mapping?

[fonsp]

I'm working on understanding and improving AddonMemory, but I don't understand what "message mapping" is, and there are do comments or docstrings. Could someone document this in the code?

[bvdmitri]

The MessageMapping is a structure that "knows" how to "map" other input messages/marginals into an output message. You can think of it as a lambda function that computes the message. It hold the information about the type of the node, the direction in which we need to compute the message, constraints, etc....everything that needs to be known in order to compute a message later (since the computation is lazy and is not performed right away). Originally it was actually just a lambda function, but this structure was introduced and was optimized to circumvent some of the Julia multiple dispatch issues with storing types as DataTypes (hence more type-unstable)

[bvdmitri]

Some info is here

[bvdmitri]

The "lambda-body" is here